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Ultrasound and vacuum were respectively employed to enhance CO2 desorption in a water scrubbing biogas upgrading system. Results showed that incomplete CO2 desorption could cause a high CO2 content in the water and seriously affect the purity of the product gas. Vacuum had a strong enhancement effect on CO2 desorption. When a vacuum of 0.04 MPa was used to enhance CO2 desorption, the amount of the stripping air could be reduced to 1/16-th of that without enhancement, indicating that vacuum could greatly enhance CO2 desorption and significantly decrease the amount of the stripping air, which was expected to reduce a large amount of energy consumption. In contrast, the enhancement effect of ultrasound was not so obvious for CO2 desorption in the desorption column with air stripping, since the solution could be well desorbed by gas stripping, though ultrasound could strongly affect the static CO2 desorption.

Vegetable waste is one of the major organic solid residues available for sustainable biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for acidogenic fermentation of wasted potato (WP). Three leaching bed reactors (LBRs) were operated at various pH values (6.0, 7.0 and 8.0) with an organic loading rate (OLR) of 6.7 g volatile solid/(L·d) and hydraulic retention time of 6 d. Butyric acid-type fermentation with butyric acid as predominant volatile fatty acid (VFA) was observed with a concentration and proportion (of total VFAs) of butyric acid, which were 7.8 g/L, 49.7 % and 9.6 g/L and 52.2 % at pH 6.0 and 7.0, respectively. Conversely, at pH 8.0, mixed acid-type fermentation was observed with acetic and butyric acid as the major VFAs. Control experiment without pH manipulation didn't perform well in VFAs production at first 6 days and then VFAs concentration increased as pH value was adjusted to 8. It was indicated that the inhibition was caused by high undissociated VFAs concentration due to low pH and the VFAs production could be improved through pH control strategy to regulate the undissociated VFAs concentration. According to the bacterial analysis, the microbial community was diverse and Firmicutes were the most important bacteria at different pH conditions. Therefore, the results suggested that a process of pH control might be feasible for stable and efficient acidogenic fermentation.

Methanogenic performance and microbial communities including both bacteria and archaea in UASB reactor treating acidogenic metabolites from acidification of ensiled corn stover (ECS) were investigated. Gradient organic loading rates (OLRs) were adopted to study the conversion of volatile fatty acids (VFAs) characterized by high concentration of acetic acid and propionic acid. The removal rate of chemical oxygen demand (COD) reached above 80.0 % at OLR of 8 g/L·d and volumetric methane production rate improved significantly as the OLR increased. When OLR was 10 g COD/L·d, acetic and propionic acids in effluent were accumulated and failure of methane production occurred. Compared with the control, the methanogenic inhibition was caused by the presence of high concentration of propionic acid. The profile of conversion of individual VFAs in UASB reactors was investigated at different OLRs. Furthermore, microbial communities in anaerobic sludge at OLR of 8 g COD/L·d were compared with those in inoculum and the shift of bacteria and archaea were analyzed. The abundances of some representative acetogenic bacteria such as Proteobacteria (14.18 %) and Bacteroidetes (11.16 %) increased obviously, which contributed to the oxidation and decomposition of organic acids. Acetotrophic methanogen (Methanosaeta) and hydrogenotrophic methanogen (Methanobacterium) played synergistic roles with acetogens to efficiently complete the VFAs conversion. This study will be of great importance to guide the application of two-phase AD of agricultural waste in full-scale plant.

Corn straw silage (CSS) is one of the organic solid residues available for biogas production. The aim of this study was to investigate the possibility and optimal controlling strategy for anaerobic digestion (AD) of CSS. Four leaching bed reactors (LBR) were operated at different pH. Maximum volatile fatty acids (VFAs) concentration of 19.34 g/L was reached at pH 8.0 with acetic and propionic acids as dominant VFAs. The subsequent microbial analysis indicated that abundant bacteria were Firmicutes, Bacteroidetes and Proteobacteria. UASB as methanogenic reactor was integrated with the LBR. The organic loading rate (OLR) could reach 8 g COD/L·d with effective conversion of VFAs. Acetotrophic Methanosaeta and hydrogenotrophic Methanobacterium played major roles in methanogenic process. In the whole process, the results showed that methane yield of 143.4 mL CH4/g volatile solid (VS) was obtained. pH and OLR controls in two-phase AD were feasible for methane production from CSS.

Biogas production from lignocellulosic hydrolysate is of great potential for lignocellulosic materials. Two-phase anaerobic digestion was proposed in this study. Acidogenic fermentation was carried out with corn straw hydrolysate as feedstock for volatile fatty acids (VFAs) production. Using anaerobic sludge (AnS), different inoculum to substrate ratios (ISRs) of 0.5:1, 1:1 and 2:1 were investigated. The highest VFAs yield was obtained at ISR of 0.5:1.VFAs composition analysis showed that butyric acid was the predominant acid, followed by acetic acid and propionic acid. The effects of AnS and aerobic sludge (AeS) on the acidogenic performance of hydrolysate were compared. The optimum VFA yields were 0.38 g/g COD-added for AnS and 0.32 g/g COD-added for AeS with HRT of 5 d, respectively. The bacterial diversities of inocula and digestates were analyzed by high-throughput sequencing. Two origins of inocula had distinct bacterial structures, but they did share core communities that included Firmicutes, Chloroflexi, Proteobacteria and Bacteroidetes at phylum level. The bacterial communities of both digestates changed significantly as compared with those in inoculum. Firmicutes was absolutely dominant in all the bacterial species. Therefore, the AeS could be an option as the acidogenic inoculum. The microbial information will be beneficial for the enrichment and acclimatization of microbes. In methanogenic process, VFAs obtained in acidogenic stage could be efficiently converted into methane. The ultimate methane yield at organic loading rate (OLR) of 8 g/L·d could reach 290 mL CH4/g COD-added and 279 mL CH4/g COD-added for AnS and AeS acidified digestate. Two-phase anaerobic digestion was proved to be suitable for bioconversion of lignocellulosic hydrolysate into biogas.

The transfer process of the in-situ coupling process of fermentation, extraction and distillation for biobutanol production was discussed from a theoretical point of view. The existence of temperature gradient in the extraction section was proved. The force of solute in the extracted liquid was discussed. And the mass transfer mechanism and impetus of the FEDIC process was analyzed. The theoretical analysis could provide a foundation for the following research.